1. Field of the Invention
The present invention relates to a color temperature estimating apparatus, a color temperature estimating method, a photographing apparatus, an exposure amount determining method, and an exposure amount determining apparatus. Particularly, the present invention relates to a method and apparatus for estimating a color temperature of a light source whose color temperature is to be estimated, a photographing apparatus using the method and apparatus for estimating a color temperature, and a method and apparatus for determining an exposure amount when an image on a photographic film is printed on a photosensitive material using the estimated color temperature.
2. Description of the Related Art
The amount of printing exposure required when a film image is printed on photosensitive materials such as photographic paper is determined according to the quantity of light received by the film from the subject at the time when the subject was photographed, and the amount of printing exposure differs from frame to frame. To obtain a print with a superior color reproductivity, it is necessary to correct a printing exposure depending on photographing conditions. To this end, as regards an exposure required when a color image is reproduced on a photosensitive material from an original color picture, a gray balance is determined by determining an integral transmission density for each of red light (R), green light (G), and blue light (B) using a photometer, which is provided with color separation filters made of dye filters or vapor deposition filters.
However, information on photographic light quality may vary depending on color failure in backgrounds or development conditions. This makes it impossible to accurately estimate light quality, and hence the color reproductivity may become poor depending on variations in the quality of light illuminating a subject. This is because judgment cannot be made as to which portions are gray on the photographic film.
The most effective method for detecting a gray portion on the photographic film is to estimate the color temperature of a photographic light source.
However, in order to estimate a color temperature of the photographic light source from the photographic film, it is necessary to separate a spectral reflection distribution of the subject and a spectral energy distribution of the photographic light source from exposure data (data obtained by converting a color development dye density into an exposure through a characteristic curve) which are recorded on the film.
Assuming that a spectral energy distribution of a photographic light source is P(.lambda.), a spectral sensitivity distribution of a film is S(.lambda.), and a spectral reflectance distribution of a subject is q(.lambda.), exposure data E can be represented by the following expression (1): EQU E=.intg.P(.lambda.)q(.lambda.)S(.lambda.)d.lambda. (1)
However, the spectral reflectance distribution of the subject varies every time of photographing, and hence the spectral reflectance distribution cannot be specified. For this reason, it is difficult to estimate the color temperature of the photographic light source from the photographic film.
For example, assuming that, as shown in FIG. 11A, the shapes of the spectral sensitivity distributions of the three sensitive layers are the same, and the spectral energy distribution of a photographic light source appears to be flat, even if E.sub.r =E.sub.g =E.sub.b =0.7 can be obtained as exposure data, it is impossible to obtain the spectral reflection distribution of the photographic light source as one distribution, as shown in FIGS. 11B and 11C.